1. Field of the Invention
The present invention relates generally to devices for washing the glass lenses or the like of headlamps of motor vehicles, by projecting a liquid thereon. The invention relates more particularly to a screen washing device comprising a spray unit having a nozzle directed towards the screen and a pump mounted between the reservoir and the spray unit and operated by a control device.
2. Description of the Related Art
Devices are already known, for example from French Pat. No. 2 372 057, in which the spray unit is designed to discharge a mist of fine droplets of liquid having the form of a cone or the like, the geometry of this discharge being such as to cover at all times the entire surface of the glass lens to be washed.
However, for a given rate of flow, such fine droplets have a very limited washing efficiency. While the dirt stains on the lens are correctly dissolved by the liquid, their removal therefrom is very poor. Moreover, the geometrical shape of the mist of droplets is highly sensitive to variations in the speed of the vehicle, so that the contours of the cone of droplets seldom correspond exactly to those of the lens.
Devices are also known for effecting the wiping of the lens surface to be cleaned.
For example, in French Pat. No. 2 222 856, the spray unit is conceived so as to allow the evolution within it of various hydrodynamic phenomena which lead either to a modification of the jet cross-section or to a change in its direction at the outlet, in which case it can cover the surface to be washed along either a sinusoidal or a spiral path. However, such a device requires a highly complex spray unit, correspondingly expensive to produce, and does not achieve uniformity of the kinetic energy of impact of the liquid over the whole area of the glass lens.
Finally, a spray unit is known from French Pat. No. 2 345 219 which is capable of generating a horizontal lamellar jet of liquid. Owing to an oscillating-turbulence phenomena within an inner chamber of the spray unit, at the outlet of the spray unit a sweeping action of the sheet of liquid over the entire height of the headlamp lens is obtained.
This type of device is disadvantageous in that the manner in which the sweeping is effected is incompatible with the desired homogenous distribution of washing energy in the direction of the width of the glass lens. To be more precise, the configuration defined at the outlet orifice of the spray unit does not allow the desired distribution other than approximately, and not for each particular height of the sheet of water.
Furthermore, the turbulence phenomena created within the spray unit to effect the sweeping action is the locus of an energy loss in the moving liquid which, for a given volume of liquid, contributes to a drop in the washing efficiency.
One object of the present invention is to remedy the drawbacks of prior techniques and to provide a screen-washing device in which the means for obtaining a sweep effect by the sheet of water confer to this sweep a more efficacious cleaning action. A subsidiary object of the invention is to supply a substantially uniform quantity of liquid to the whole of the surface of the glass lens to be washed.